1. Field of the Invention
The present invention relates to a spindle motor suitable for a disk driving device for such as hard disk drive, optical disk drive and removal type of disk drive.
2. Related Art
FIG. 1 is a sectional view of a spindle motor for disk driving device. This spindle motor is used for a so called a removal type of disk drive (ZIP), in which a disk i.e. a recording medium can be replaced upon necessity. And, the spindle motor of FIG. 1 is a so called “shaft rotation type” of spindle motor, in which a shaft 2 is mounted on a rotor 1, the shaft 2 is supported on a housing 5 through a bearing 3.
The rotor 1 comprises a circular disk putting face 1a, around its circumferential end portion, a downwardly depending flange 1b is formed in unitary manner. And, on an inner wall of the downwardly depending flange 1b, a magnet 1c is mounted. In the illustrated example, although the shaft 2 is pressed in and fixed on the central portion of the rotor 1, there is another example in which the shaft 2 is formed in a unitary manner with the rotor 1. Now, since the spindle motor shown is for a ZIP, on the disk putting face 1a too, a magnet 1d for functioning as a disk clamper is provided.
Further, in the spindle motor shown in FIG. 1, in order to increase a rotation precision of the rotor 1, two bearings 3 are used so as to clamp a spacer 4. In the housing 5 with a cylindrical projection portion 12 to be fixed with an outer ring of the bearing 3, a stator 6 is fixed with a coil 6a and stack 6b. A lead wire 7 to supply electricity to a coil 6a supported at the stator 6 is connected to a flexible printed circuit board (FPC) 8 through an opening 5a formed on the housing 5. Further, the spindle motor for disk driving device comprises identical structure in general not limited to the one for ZIP.
Now, recently the operation speed of computer has been increased greatly, accordingly to an information memory medium such as disk drive a further increased capacity has been requested. In general, in order to increase a memory capacity per disk, it is necessary to narrow a track width for writing and reading. However, if a rotation deflection of a spindle motor is great, it becomes difficult to trace such track by the head for writing and reading. In other word, it becomes quite important to increase the rotation precision of the spindle motor so as to increase the memory capacity of the disk driving device. So that, a high precision of parts are requested for components of the spindle motor, and a housing 5 as a basic structure of the spindle motor has been prepared by applying a cutting work by using a NC working machine to a metal material such as aluminous and ferrous materials.
However, a housing to be prepared by cutting work is not preferable in view of a cost reduction. Initially, the cutting work itself is evaluated highly priced from the viewpoint of cost reduction in a mass production. Further, since a surface treatment for corrosion protection is indispensable due to a metal-made, the cost reduction has been made difficult.
Further, although a conventional spindle motor has been developed to increase the rotation precision as a primary target, due to the recent time's demand, it has been mentioned as a problem to be solved to reduce a rotation noise.
The present invention has been made in the light of the above problem, the purpose thereof is to reduce the cost of the components of the housing of the spindle motor and also to diminish the rotation noise of the spindle motor. In addition, further increase of the rotation precision of the spindle motor is intended.